1. Field of the Invention
The present invention relates to a solid-liquid separator using a roller system, equipped with rollers each having a screen formed in the outer periphery thereof with plural pores, for separating a solid-liquid mixture into a solid component and a liquid component via the plural pores.
2. Description of the Prior Art
There has heretofore been known a solid-liquid mixture separator for separating liquid through filtration from a solid-liquid mixture having a solid substance and a liquid substance mixed with each other, in which cited as the solid-liquid mixture is a solid-liquid mixture (so-called “boiled soybean-water slurry” that is hereinafter referred to also as “soybean soup” in the description) as obtained through boiling of soybean slurry (so-called unheated soybean-water slurry) that has been acquired by immersing soybeans in water overnight and then scrubbing and crushing the soybeans while being added with water when manufacturing tofu or fried bean curd.
As a separator for a solid-liquid mixture, there are a screw-system one comprising a cylindrical screen having plural pores formed therein and a spiral screw driven and rotated within the cylindrical screen and a multistage-system one comprising the screw-system one and a cylindrical screen that has plural pores formed therein for gravity filtration (a screen for filtration) (Japanese Patent No. 3417794 or 3392322, for example). On the other hand, there is a roller-system one in which a solid-liquid mixture is supplied between a pair of right and left rollers facing each other, with their respective axial directions kept in parallel. Japanese Patent No. 3537377 (hereinafter referred to as “Citation 3”) points out that one extraction can only be attained with the pair of rollers and performs squeezing with the pair of rollers (primary extraction) the solid-liquid mixture (soybean soup) supplied from above the pair of rollers and squeezing, with the lower surfaces of the rollers and a retention portion (secondary extraction), okara received on the retention portion with which an extraction passageway formed so that the amount to be discharged may be smaller than the amount to be received communicates. In the embodiment of Citation 3, as shown in FIG. 11, the retention portion 5 for okara (a solid substance) is formed so as to be surrounded by the pair of rollers 1, scrapers 4 for scraping the solid component adhering to the rollers, and opposing lower side surface portions 16a extending from opposing central portions 17 of the rollers 1 to the scrapers 4 and, at this retention portion 5, a squeezing passageway 50 having a passageway narrowed so that the amount to be discharged may be smaller than the amount to be received for giving squeezing pressure to the retained okara is formed. Incidentally, the squeezing passageway 50 has a discharge outlet 51 provided with a lid body 53 biased with a spring 52 in the direction of closing the discharge outlet 51. The lid body 53 enables the opening area of the discharge outlet 51 to be varied in accordance with the internal pressure of the retention portion 5.
While the solid-liquid separator using the roller system has the advantage of making it possible to treat a great mount of a solid-liquid mixture in a short period of time, the system capable of acquiring high-quality soymilk from soybean soup is the gravity filtration system disclosed as an appropriate system in Japanese Patent No. 3417794 or 3392322 concurrently using a gravity filtration portion. An ordinary solid-liquid separator using the roller system generally performs the extracting treatment by the use of the pair of rollers. Though Citation 3 also performs the extracting treatment using the pair of rollers, it performs filtration (dehydration or squeezing) under strong pressure at positions between the pair of rollers and below them in the presence of the retention portion 5 and squeezing passageway 50.
In Citation 3, however, though it is intended that the pair of rollers are used to squeeze (primarily extract) the solid-liquid mixture (soybean soup) and that a solid component (okara) received on the retention portion, with which the squeezing passageway formed so that the amount to be discharged may be smaller than the amount to be received (i.e. interpreted in Citation 3 as a structure in which the cross-sectional area of the outlet is narrowed to be smaller than that of the inlet of the passageway) communicates, is subjected to secondary extraction with the lower surfaces of the rollers and retention portion, the flow rates of the liquid component (soymilk) and the solid component (okara) fluctuate in accordance with the state of variation in viscosity of the soybean soup, resulting in fluctuation in internal pressure and, in accordance with it, resulting in a variation in the degree of extraction of okara and in the quality of soymilk. It is necessary that the degree of squeezing of the squeezing passageway be set to be optimum for the concentration and product of the solid-liquid mixture and, depending on a case, closure or clogging may possibly be induced. In addition, in order to appropriately perform the primary and secondary extractions, it is necessary to adjust the rotation speed of the rollers, adjust the set positions between the paired rollers 1 and the scrapers 4 constituting the retention portion 5 and narrowing the passageway so that the amount to be discharged be smaller than that to be received. These settings and adjustments are also difficult to perform. The degree of squeezing of the squeezing passageway corresponds to the degree of internal pressure and, though it is necessary in nature to set optimum degrees depending on the solid-liquid mixture (concentration, viscosity, etc.) or the product (tofu or fried bean curd), problems have been entailed in that the fixed degree of squeezing has made it difficult to exchange a product, that a large content of a residue to be mixed therein has made the quality of the fried bean curd worse and, as the case may be, closure or clogging has arisen. Incidentally, though the discharge outlet 51 of the squeezing passageway 50 is provided with the lid body 53 biased with the spring 52 in the direction of closing the discharge outlet 51, a cumbersome labor of interchanging springs has been required in the case where a different degree of squeezing is to be set depending on a difference in product (between tofu and fried bean curd, for example) and, since the position of the spring to be attached is deep in the lower side of the apparatus, visual contact, gap adjustment (measurement) or cleaning working has been difficult to perform. These are faults. An additional fault has lain in that a mistake made in attaching or detaching the lid body 53 possibly mars the expensive screen of the roller. Citation 3 merely discloses in the figure thereof that the lid body is wedge-shaped and no detailed description on the disposition thereof is made therein (there is no description therein as to whether the lid body can fully be closed or as to the cleaning property thereof). Incidentally, since the lid body is made slender and wedge-shaped and since the aperture of the narrow discharge outlet is adjusted, it is possible to exert appropriate internal pressure even with a spring having a small spring coefficient. The actual tendency, however, is to exert more internal pressure than necessary, thereby increasing the amount of the residue to be mixed in soymilk to possibly entail a problem of deteriorating the quality of products.
Even in a conventional ordinary roller-system solid-liquid separator, the properties (fluctuation in water content resulting from the degree of pressure to be exerted) of the solid component (okara) to be discharged always vary depending on the rotation speed of the rotary rollers, configuration of the rollers (a difference in size among the plural pores), ratio of the solid content in the solid-liquid mixture, concentration of the liquid content, etc. However, this does not result in complete separation of the liquid component by desirable homogenous filtration, but induces a difference in amount of a minute solid substance (residue in the case of soymilk) in the liquid component and a change in higher-order structure and emulsified state of a polymer (protein etc.) in the components to affect the quality of products more or less. Though it has been known in the tofu industrial field that fried bean curd or deep-fried tofu produced from strongly extracted soymilk has, through experiences, turned red to thus induce product inferiority, this fails to stably separate the liquid component (soymilk) of desirable high quality through homogenous filtration.
In view of the above, the object of the present invention is to provide a solid-liquid separator using a roller system, which is capable of stably separating a solid-liquid mixture into a solid component and a liquid component at all times under homogeneous pressure without being affected by a change in internal pressure resulting from fluctuations in the amount of the solid-liquid mixture to be supplied and in the viscosity of the solid-liquid mixture and which is difficult to clog by a solid substance, easy to adjust the degree of squeezing and easy to perform cleaning working.